According to new isotopic dating and DNA experiments, the mummies—a male and a female—were assembled from various body parts, although the purpose of the gruesome composites is likely lost to history.

The mummies were discovered more than a decade ago below the remnants of 11th-century houses at Cladh Hallan, a prehistoric village on the island of South Uist (map), off the coast of Scotland.

The bodies had been buried in the fetal position 300 to 600 years after death. (See bog body pictures.)

Based on the condition and structures of the skeletons, scientists had previously determined that the bodies had been placed in a peat bog just long enough to preserve them and then removed. The skeletons were then reburied hundreds of years later.

Terry Brown, a professor of biomedical archaeology at the University of Manchester, said there were clues that these bog bodies were more than they seemed.

On the female skeleton, "the jaw didn't fit into the rest of the skull," he said. "So Mike [Parker Pearson, of Sheffield University] came and said, Could we try to work it out through DNA testing?"

Brown sampled DNA from the female skeleton's jawbone, skull, arm, and leg. The results show that bones came from different people, none of whom even shared the same mother, he said.

The female is made from body parts that date to around the same time period. But isotopic dating showed that the male mummy is made from people who died a few hundred years apart.

Quick Dip in the Bog

Another clue to the odd nature of the Cladh Hallan mummies is their unusually well-preserved bones.

A peat bog is a high-acid, low-oxygen environment, which inhibits the bacteria that break down organics, said Gill Plunkett, a lecturer in paleoecology at Queen's University Belfast who was not involved in the current study.

In the Cladh Hallan bodies, the bones are still articulated—attached to each other as they would be in life. This suggests that the buriers removed the bodies from the peat bog after preservation but before acid destroyed the bones.

When the mummies were later reburied in soil, the soft tissue again began to break down.

The researchers aren't sure why the villagers went through this unusual process, or why they built composite mummies in the first place.

A cynical theory, study author Brown said, assumes that the Bronze Age people of Cladh Hallan were just eminently practical: "Maybe the head dropped off and they got another head to stick on."

Another possibility is that the merging was deliberate, to create a symbolic ancestor that literally embodied traits from multiple lineages.

Brown cites the example of the Chinchorro mummies discovered in the Chilean Andes, where embalmers reinforced or reconstructed bodies with sticks, grass, animal hair, or even sea lion skin. (Also see "Prehistoric Mummies Poisoned.")

"It seems the person is not so important, but the image is. So it's not a single identity, but it's representing something."

More Combo Mummies Out There?

According to Brown, there may be other composite bodies waiting to be discovered.

Often when scientists study the DNA of very ancient remains, they sample only one part of a body to prevent needless damage to the skeleton.

Additional composite bodies, if they exist, are likely to come from such long-ago time periods.

"I think you'd have to go back to a time when the rituals were more bizarre," Brown said. "You'd have to go back to the mists of unrecorded time."